The number of acute kidney injuries is increasing, a study finds. / Robert Hanashiro, USA TODAY

by Karen Weintraub, Special for USA TODAY

by Karen Weintraub, Special for USA TODAY

Acute kidney injuries have more than doubled since 2000, causing nearly 39,000 deaths in 2009 alone, according to a new study.

Severe infections, heart failure, trauma, bad reactions to medication or surgical complications can all cause sudden declines in kidney function, but it's not yet clear which - or which combinations - of these is driving the 10% annual rise.

It's possible, researchers say, that some newer medications are damaging kidneys, or that pneumonia strains are getting more dangerous. Or maybe it's simply that treatments for other diseases, such as sepsis infections and respiratory failure, are getting better, while treatment for acute kidney disease isn't.

"That would be my guess," says Ramon Bonegio, who studies acute renal failure at the Boston University School of Medicine and is an attending physician at Boston Medical Center.

There are no drugs to reduce the incidence or severity of acute kidney injuries, though several are under development, says Bruce Molitoris, president of the American Society of Nephrology.

In the new study, published Thursday in the society's journal, researchers reviewed 1.9 million U.S. hospitalizations due to acute kidney injuries. Only the most serious injuries, which required patients to go on dialysis, were counted.

Although acute kidney disease is far more common among African Americans than whites, the study found that increases were consistent across races, genders and from middle age up, says Raymond Hsu, a study author and research fellow in the division of nephrology at the University of California-San Francisco.

Molitoris, also a professor of medicine at Indiana University, says he was surprised by the high rate of increase Hsu found but does not doubt his conclusions.

"I think awareness is a big issue," Molitoris says. "It's an under-recognized major complication in the hospital."

Hsu and Molitoris drew a distinction between the acute kidney injuries that were the subject of this study and the chronic kidney disease that can come with diabetes, hypertension or immune conditions - although chronic kidney disease can lead to acute injuries.

With chronic kidney disease, which affects a quarter of those over 60, once a patient needs dialysis, the kidneys have been damaged beyond repair. In acute kidney injury, dialysis is meant to be temporary, until the kidneys can recover their ability to filter the blood. Nearly one-quarter of those with acute kidney injury die before they can be taken off dialysis.

Hsu says the high death rate suggests that dialysis may be overused in some of the sickest patients, who should be given a choice - before they're acutely ill - about whether to pursue a painful procedure that may do little to extend their lives.

"Would they want those invasive measures?" asks Hsu. "By the time they reach us, they are already too sick to express those wishes."

Hsu says he next hopes to study patients who do well after an acute kidney infection and dialysis, to better understand their recovery process and translate it to those with worse outcomes.